Humidity doesn’t affect cricket ball swing

By wiredchop

This July sees the next biannual conference on Sports Engineering, held at the University of Massachusetts, Lowell. The conference always has a lot of interesting papers on the subject of engineering and technology in sport. Thanks to the internet age, the papers at this conference are also available online for anyone to read.

Before the conference even began, one of the papers caused quite a stir, with several online blogs and news sites reporting on the findings. The paper is by our own Dr David James and Dr John Hart (in Collaboration with Danielle Macdonald)  and investigates the effect of humidity on cricket ball swing. Dr James studied cricket ball dynamics for his PhD and he continues to research into the behaviour of the ball and various factors which have an effect.

Dr James et al.’s paper looks specifically at humidity and its effect on cricket ball swing. Swing bowling is utilised in cricket to cause the ball to swerve on its way to the batter and make it more difficult to hit. Cricket folklore states that the ball will swing more on cloudy, humid days. However, the aerodynamic theory which explains why a cricket ball swings states that the lower density air at high humidity should create less ball swing. The team also looked at how high humidity affects the cricket ball (changes in shape and mass) to see if this could provide an explanation for the perceived increase in spin. They found no evidence to suggest a cause.

So this paper suggests that the increase in swing on humid days is in fact a myth, there is no effect, or that there is an entirely different mechanism responsible.

You can find the paper here.

Laser scan of cricket ball

A laser scan of a cricket ball looking at changes in dimension which might be responsible for increased swing.

About wiredchop

Simon Choppin Simon’s sports engineering career began at the age of six when he loosened the wheels of his skateboard in order to make it go faster. While the experiment was chalked up as his first failure, his resulting dimpled skull has provided an aerodynamic advantage in more recent sporting pursuits. Academically, Simon completed a degree in Mechanical Engineering with Mathematics at Nottingham University before joining the Sports Engineering Research Group at Sheffield to start his PhD. His main interests include work with high speed video, mathematical modelling of various sorts and experimental work involving machines with big buttons. As a sportsman, Simon has an unfortunate lack of talent for anything requiring skill, tactical awareness or the ability to learn from mistakes. He does however seem to posess the ability to move his legs around for a long time until other people get tired, for this reason you’re most likely to see him on a bike of some sort or running up a hill in offensively small shorts. Simon was fortunate enough to have a stint at the Guardian newspaper as part of the BSA’s media fellowship, which gave him the idea for this blog. Other than this, his writing experience includes his PhD thesis and various postcards to his Mum.